(Bloomberg) — Elon Musk’s Boring Co. raised $113 million in equity to dig tunnels and develop a high-speed transportation system known as the hyperloop.

The startup disclosed the investment in a U.S. securities filing on Monday. The financing round included 31 unnamed investors, according to the Securities and Exchange Commission document. Boring Co. has said Musk is its primary backer and that it doesn’t plan to seek public funding. A spokesman didn’t immediately respond to a request for comment.

In addition to the private stock sale, Musk is funding his underground transit plans with the sale of merchandise. Boring Co. sold 50,000 hats and 20,000 flamethrowers to Musk fans. The flamethrowers generated $10 million in revenue.

Musk, the billionaire technologist who also runs Tesla Inc. and Space Exploration Technologies Corp., first unveiled his idea for a hyperloop — a tube-based system to move people from San Francisco to Los Angeles in a half hour — in a 57-page white paper in 2013 because he was frustrated with California’s plans for a high-speed rail system. Boring Co. was ultimately founded to “solve the problem of soul-destroying traffic,” and the company’s website said it’s pursuing projects in Los Angeles and the Baltimore-Washington area, as well as the potential express route from Chicago’s Loop to O’Hare International Airport.